There are two duplex modes for mobile communications systems: frequency division duplex (Frequency Division Duplex, FDD) and time division duplex (Time Division Duplex, TDD). In an FDD system, different frequency bands are used for receiving and sending. However, in a TDD system, different times are used for receiving and sending on a same frequency band.
As uplink services and downlink services become more asymmetric in a communications system and a ratio of the uplink services to the downlink services change with time, in a conventional Long Term Evolution (Long Term Evolution, LTE) system, use of fixed paired spectrums in FDD and fixed uplink-downlink timeslot allocation in TDD can no longer effectively support the dynamic asymmetry feature of the services. In addition, because a total volume of uplink and downlink services grows explosively, a half-duplex mode can no longer meet requirements in some scenarios, and a full duplex mode becomes a potential technology. In the flexible full duplex, the growth of the total service volume and the asymmetry feature are fully considered, and uplink resources and downlink resources can be adaptively allocated based on distribution of uplink services and downlink services. In this way, TDD, FDD, and full duplex are organically integrated, and system resource utilization is effectively improved, so that a future network requirement is met.
In a flexible frequency band technology, some uplink frequency bands in an FDD system are configured as “flexible frequency bands”. In actual application, based on distribution of uplink services and downlink services in a network, “flexible frequency bands” are allocated for an uplink transmission or a downlink transmission, so that uplink and downlink spectrum resources match uplink and downlink service requirements, and spectrum utilization is improved. As shown in FIG. 1, when a downlink service volume is higher than an uplink service volume in a network, a frequency band f4 originally used for an uplink transmission may be configured as a frequency band used for a downlink transmission in the network. In a flexible duplex technology, TDD may be used on the frequency band f4 to transmit uplink and downlink services. Because there are seven different subframe configuration modes in a TDD mode, when different TDD configurations are used in neighboring cells, cross timeslot interference may occur in the neighboring cells. As shown in FIG. 2, in a timeslot in which a macro cell sends a downlink signal, a femto cell is used to receive an uplink signal. Consequently, a base station to base station interference occurs between the two cells: The downlink signal from a base station in the macro cell is directly received by a base station in the femto cell, and this severely affects quality of an uplink signal received from an L-UE (Local UE, L-UE) by the femto cell.
In an LTE system, when an evolved NodeB (evolved NodeB, eNB) schedules user equipment (User Equipment, UE), in order that the eNB selects an appropriate frequency resource, an appropriate modulation and coding scheme (Modulation and Coding Scheme, MCS), and the like so that the UE can better receive data, the eNB sends a downlink reference signal in all bandwidths of a cell, and then the UE measures CSI of a cell-specific reference signal in all or some bandwidths according to an upper-layer indication and feeds back the CSI to the eNB. The eNB selects an appropriate time frequency resource and an appropriate MCS based on the CSI reported by the UE, and transmits downlink data. In the foregoing technology, the UE reports uniform CSI to all downlink subframes. For example, in a specific CSI reporting period, the UE may select one downlink subframe for CSI measurement and reporting. However, if cross timeslot interference occurs between the neighboring cells, interference between different downlink subframes may be different. For example, in a cell, interference to the cell in one downlink subframe may be downlink interference from a neighboring base station, and interference to the cell in another downlink subframe may be uplink interference from UE served by a neighboring base station. In the foregoing case, if the UE still reports uniform CSI, the base station cannot learn an interference difference between different downlink subframes, and the base station cannot select an appropriate frequency resource, an appropriate MCS, and the like to transmit data. This reduces resource utilization.